Lanthanide complexes with a new luminescent iminophosphonamide ligand bearing phenylbenzothiazole substituents

Abstract

A new iminophosphonamine Ph₂P(HNPbt)(NPbt) (1, HL) bearing chromophore 2-(phen-2′-yl)-1,3-benzothiazole (Pbt) substituents was synthesized and introduced into lanthanide complexes. It was found that salt metathesis reactions between KL (2) generated in situ and LnCl₃ lead to the formation of tris-iminophosphonamide complexes [LnL₂]L (Ln = Y (3), Sm (4), Gd (5), Dy (6)), regardless of the 2/LnCl₃ ratio. Compounds 3–6 consist of a cationic fragment [LnL₂]⁺, where the lanthanide atom is surrounded by two rigidly κ⁴-coordinated ligands, and an L⁻ anion residing in the outer coordination sphere. Iminophosphonamine 1 shows a rare excitation wavelength-dependent two-band luminescence in the solid state. For compounds containing the deprotonated form, namely potassium salt KL and complexes of Gd and Dy, a single-band luminescence with the color changing from turquoise to orange was observed. The Sm complex reveals a set of a few narrow well-resolved bands corresponding to the f–f transitions against the background of the outer-sphere ligand's emission.